The vacuum booster is a boosting device for the automobile brake system. The function is to amplify the pedal input force to reduce the braking force applied by the driver. The principle is that the booster has a front cavity and a rear cavity separated by a valve body diaphragm and a diaphragm tray. The two cavities are kept in a vacuum state by a vacuum pump or an auxiliary vacuum pump of the engine intake manifold, and a pressure difference is formed by controlling the vacuum degree of one cavity, so as to achieve the boosting effect.
During usage, the brake takes effect only when the driver overcomes the starting force, thus the assembly plant wishes the starting force to be small. Meanwhile, the restoring force can help the pedal to return, thus the restoring force is hoped to be large. But the prior art vacuum boosters disclosed by the Chinese Patent CN 102923113 A (publication date: Feb. 13, 2013), has a problem in that the restoring force is small.
Starting force, as used in the subject disclosure, includes a minimum input force when the vacuum booster starts generating an output force.
Restoring force, as the term is used in the subject disclosure, occurs during the continuous decrease of an input force of the vacuum booster, and includes the input force obtained when the output force is decreased to zero.